Ed Koch had a piece on the political website Real Clear Politics recently that should worry President Barack Obama. Koch, who backed Obama in the 2008 election, wrote that “If President Obama does not change his position [on Israel], I cannot vote for his reelection.”One might think that the vote of one octogenarian and often cranky former New York City mayor may not be a big deal, but Koch has a long and eventful history of involvement with presidential campaigns. He almost perfectly captures the views of a certain type of older—often but not always Jewish—Democrat who is nonetheless skeptical of his party on national security issues. While Koch usually backs his party’s candidate, he also seems to have an uncanny ability to back a Republican—tacitly or explicitly—when the Democrats are going to lose.In 1980, during his first term as mayor, Koch tortured Jimmy Carter over Carter’s position on Israel. At one point, Carter’s people reached out to Koch and asked him not to say anything about a particular administration action until the president had had a chance to explain himself. Koch obliged and went down to the White House for a meeting with Carter. Unsatisfied with the explanation Carter gave, Koch then continued criticizing the administration, infuriating Carter. In Carter’s White House Diary, he recalled that “Ed Koch made a disgraceful statement in New York, referring to [Secretary of State Cyrus] Vance, [National Security Adviser Zbigniew] Brzezinski, [U.N. Ambassador Donald] McHenry, and [Assistant Secretary of State Harold] Saunders as a Gang of Four out to destroy Israel. Cy called him and had some heated words. Koch is almost acting like a fanatic this last couple of days.”As Carter stumbled toward his 1980 electoral drubbing, Koch demonstrated a particular skill at getting under the president’s skin. Koch later recalled that Carter pulled him aside at a fundraiser and said, “You have done me more damage than any man in America.” One of Carter’s aides told Koch that what was going on inside Koch’s head was more hotly discussed in Washington than the thinking of the Ayatollah Khomeni.Koch never actually pulled the lever for Ronald Reagan. “I never voted for him, but I loved him,” Koch wrote. In his book Mayor, Koch recounts an appearance with President Reagan at which Koch said: “I am not here to defend Ronald Reagan. But I’ll tell you, I like him. He’s a man of character.” Koch’s approach to Reagan differed from that of Democratic Detroit Mayor Coleman Young, who had denounced Reagan on the same day that Koch praised him. Koch recalls that the difference was not lost on Reagan aide James Brady, who told Koch, quite pointedly, “Now, which one of them do you think we’ll try to help more?” Koch even ran for reelection on the Republican ticket in 1981, although he ran as a Democrat as well. He won overwhelmingly.Koch was not nearly as sympathetic toward the next Republican president, George H.W. Bush, or to his Secretary of State, James Baker. It was Koch who revealed to the world in a newspaper column Baker’s now infamous remark regarding Jews: “F— ’em. They didn’t vote for us.” Bush himself took notice of the column, writing in a letter to Koch that “I never ever heard such ugliness out of Jim Baker.” (Perhaps he hadn’t, but Koch’s source, the late Jack Kemp, apparently had.) This incident harmed Bush among Jews, but more broadly as well. Bush won only 11 percent of the Jewish vote in 1992, a significant drop from the 39 percent Reagan had attained in 1980. Not coincidentally, with Koch on his case, Bush lost his reelection bid in 1992 to Bill Clinton, whom Koch both “supported and admired.”The next time Koch bucked his party to back the Republican presidential candidate was also the next time that the Republican candidate won the popular vote. In 2004, Koch backed George W. Bush over John Kerry because of Bush’s stances on the War on Terror, on anti-Semitism, and on Israel. “I believe the issue of international terrorism trumps all other issues,” Koch said and added that he did not “believe the Democratic Party has the stomach and commitment to deliver on this issue.” The anti-Semitism issue was also important. Bush had selected Koch to head the U.S. delegation to an Organization for Security and Cooperation in Europe conference on combating anti-Semitism in Berlin in 2004. On the third key issue, Israel, Koch wrote that he was “convinced that President Bush will never trade Israel’s special relationship with the U.S. in exchange for political support, be it domestic or international.” At the same time, he “doubt[ed] that John Kerry and the ‘Deaniacs’ who now embrace him would have the same resolve.” Koch added that “most Jewish leaders will concede that of all U.S. presidents, Bush 43 has been the most supportive and protective of the security of the State of Israel.”In contrast to his more tacit support for Reagan, Koch explicitly endorsed Bush, as he said repeatedly, “even though I don’t agree with him on a single domestic issue,” and spoke on Bush’s behalf in Jewish enclaves in Florida. Koch’s efforts helped Bush improve his showing in the Jewish vote from 19 percent in 2000 to 25 percent in 2004. This improvement in the Jewish vote contributed to Bush’s victories in both Florida and Ohio, two states without which Bush would not have been reelected.While some Democrats dismissed Koch as a turncoat after 2004, he remained in his mind a loyal Democrat. Although he had supported Hillary Clinton in the 2008 Democratic primaries, he endorsed Barack Obama in September of that year. In a prepared statement, Koch said he “concluded that the country is safer in the hands of Barack Obama. Protecting and defending the U.S. means more than defending us from foreign attacks. It includes defending the public with respect to their civil rights, civil liberties and other needs.” And while he had liked certain Republicans in the past, his good feelings did not extend to vice presidential candidate Sarah Palin, who “fails miserably with respect to her views on the domestic issues that are so important to the people of the U.S., and to me.” In addition, he noted: “Frankly, it would scare me if she were to succeed John McCain in the presidency.”But as Jimmy Carter learned in the 1970s, getting Koch’s endorsement and maintaining his support are very different things. The first indications of trouble came in an August 2009 Koch column on Real Clear Politics titled “Falling Out of Love with Barack Obama.” In this item, Koch’s concern was not Israel or a security-related issue, but Obama’s approach to health care. Koch expressed concerns about losing “the continued right to purchase and have available insurance that will permit me, no matter my age and physical condition, to purchase with my own money all the medical care I can afford.” His concerns at the time were not enough to drive him away from Obama, though. He saw “falling out of love” as “hopefully, a reversible process.” Indeed, as recently as April 25, he wrote, “I now believe President Barack Obama will be reelected, and although anything can happen between now and Election Day, I expect to be casting my vote for him.”Koch’s latest piece, however, makes it seem as if the process of falling out of love may now be close to irreversible, especially after the events of the last week. Obama’s tough speech on Israel was followed immediately by strong criticism of Obama even from Democrats and an overwhelmingly positive bipartisan reception for Israeli Prime Minister Benjamin Netanyahu’s speech to a joint session of the U.S. Congress. Obama not only lost some face in the back and forth, but he appears to have lost Koch’s backing as well. Given Koch’s long and accurate record of picking presidential winners, this could portend poorly for the president. We are still a long way from the 2012 election, and the Republican field is far from set, but Obama should beware. When Ed Koch goes against his party’s presidential candidate, it is often a very bad sign.Tevi Troy, a senior fellow at the Hudson Institute, was a senior White House aide in the George W. Bush Administration.